It is well known in motor vehicles to provide an air bag module for protecting a vehicle occupant. It is also generally known to provide an air bag module including an inflatable restraint cushion and an inflator for discharging gas to inflate the cushion upon sensing predetermined vehicle conditions. It is also known to provide air bag modules including cover elements overlying an inflatable restraint cushion and inflator in a stored position within the module wherein the cover elements include tear seams which open upon application of pressure by the inflatable restraint cushion during inflation such that the inflatable restraint cushion exits the module through the torn cover element.
Tear seams within prior cover elements have taken the form of: (i) scored grooves on the inner or outer surface of the cover; (ii) rows of spaced grooves on the inner surface of the cover with the grooves being closer together near the center of the cover and further apart at locations removed from the center of the cover; (iii) a continuous groove on the inner surface of the cover with the groove being deeper in portions near the center of the cover and shallower at locations removed from the center; and (iv) interconnected grooves consisting of spaced deeper grooves of substantially uniform size and shape with shallower grooves in the spaces between the deeper grooves with the deeper grooves being closer together near the center of the cover and spaced further apart at locations removed from the center.
As will be appreciated, the presence of scored grooves on the exterior of the cover may be aesthetically displeasing. When the tear seams are formed on the inner surface of the cover so as to reduce their visibility, the prior art has advocated the preferential concentration of grooves either in terms of numbers or height at the center of the cover with such concentration diminishing at locations removed from the center. Such preferential concentration of groove elements at the center of the cover may give rise to a substantial thinning of the overall cover thickness at the center which may make the cover subject to damage by externally applied forces thereby requiring premature replacement of the cover. Moreover, the high concentration of groove elements at the center of the cover may give rise to a shadowing affect which may cause the lines of fracture to be made visible to the vehicle occupants.